It is commonly known in the art that the ambient or background noise levels experienced by people every day may be both harmful and distracting. The noise of burglar alarms, jackhammers, buses, trains, heavy commuter traffic and construction sites in large city and urban areas can aggravate residents and commuters alike.
Users of portable music players such as MP3 players generally have the volume of their headphones raised to “block out” the ambient noise of the environment they find themselves in. Long-term use of such music players at high volumes can damage hearing. Furthermore, listening to music players at high levels when walking or cycling through city centres and urban areas inhibits other senses from functioning optimally such as being aware of traffic, other cyclists and pedestrians, which is a key sense to have functioning optimally in a busy city centre where traffic is a potential, and sometimes fatal, hazard.
Furthermore, in industry the welfare of workers who are exposed to levels of excessive noise in the workplace is important. The use of ear muffs, ear plugs and the like are commonly required by those workers to protect their hearing. However, the wearing of such ear protectors may also inhibit the wearer's awareness of their surroundings which could lead to accidents occurring in the workplace.
The use of materials in energy absorbing compositions is known, for example as disclosed in WO 2007/079320 (Sereboff). The composition is a substantially non-elastic incompressible composition, which does not quickly self-level under standard operating conditions and provides an incident energy absorbing property, wherein the incident energy may include sound energy. The applicants of WO 2007/079320 also claim that the composition may be used as an effective barrier against low frequency, high-energy sound in, for example, headphone housings, speaker housings, soundproofing in walls or submarine engine rooms. However, the compositions of WO 2007/079230 are restricted to Bingham materials, which will not flow until stress can be applied and a certain value, the yield stress value, is reached. Beyond this point the flow rate increases steadily with increasing shear stress. In essence a particular minimum value has to be achieved to activate the material.
Thixotropic materials can be composed of a number of combinations, some of which are listed in this document and can be tailored to specific frequency and decibel adapted limits but all would be structured to suit biological protection from an early sound level stage while still allowing normal conversation and safety discussion to be maintained between co-workers when on-site. As well as this, immediate activation by pre-agitation or loud sound induction would make for a highly effective responsive invention.]
Dilitant materials are also known from the prior art as being used in hearing protection ear cups where external noise is prevented from passing directly through the ear cup itself (US 2003/0034198). Furthermore, the use of particles with mis-matched characteristic acoustic impedances embedded within a matrix of a material that can support shearing loads, propagates energy diffusion thereby providing acoustic and vibration damping (U.S. Pat. No. 5,400,296). However, dilitant materials become denser when exposed to high shear/mechanical forces such as energy waves. The denser the material, the easier it is to conduct the vibrations and hence the sound travels faster and more efficiently. This can be seen clearly in a simple dilitant material such as corn flour and water. When left in a container, it is liquid but attempt to stir it and it hardens up. If you go so far as to try and lift it out, it will go solid and as long as you continually move it between your hands, it will stay solid but the moment you leave it alone, it will return to liquid form and drip through your fingers. As such, dilitant materials are not effective sound absorbing materials due to the fact that they harden when exposed to energy waves.
A protective helmet comprising a rigid shell, an inner lining with at least one inflatable cell and inflation/deflation means is known from the prior art, as described in UK Patent Application No. GB 2 340 281. The inflatable cell may be filled with a fluid having thixotropic properties using a manual or electronic-powered pump. A method for obtaining rubber ear plugs is described in U.S. Pat. No. 3,782,379, where vulcanizable rubber is used at a certain viscosity to provide thixotropic properties.
There is a need therefore to provide inner and external ear protectors and/or inner- and outer-ear headphones which do not impact on the user's awareness of their surroundings while at the same time reducing or eliminating external ambient noise. The present invention intends to address at least one of the problems mentioned above.